Beam generation and steering with integrated optical circuits for light detection and ranging

ABSTRACT

An integrated photonic beam steering device includes a planar photonic substrate. An input waveguide is configured to accept an electromagnetic energy from a source of electromagnetic energy radiation. A first splitter is configured to split the electromagnetic radiation into one or more paths. One or more phased array rows are optically coupled to each of the one or more paths. Each phased array row includes a row splitter configured to split the each of the one or more paths into two or more row paths. Two or more phase modulators are each optically coupled respectively to each of the two or more row paths. Two or more output couplers are optically coupled respectively to each phase modulator output of the two or more phase modulators. The two or more output couplers are configured to radiate a steered photonic beam away from the integrated photonic beam steering device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of co-pending U.S.provisional patent application Ser. No. 61/084,508, filed Jul. 29, 2008,which application is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The invention relates to optical phased arrays in general and moreparticularly to an optical phased array that employs planar integratedstructures.

BACKGROUND OF THE INVENTION

LIDAR (Light Detection and Ranging) and LADAR (Laser Detection andRanging) are methods used to image and characterize remote objects.LIDAR and LADAR are referred to interchangeably herein as “LIDAR”. Intypical LIDAR applications, an electromagnetic beam in the opticaldomain or mid to near infrared domain (about 10-400 THz) is sweptthrough the field of view of a detector.

Electronic countermeasures are not LIDAR per se, but use some of thesame concepts relating to beam steering. In some electroniccountermeasures, a very strong directed infrared beam is used to confusethe electronics of a guidance or homing system (e.g. of a heat-seekingmissile) or to confuse another hostile detection system by providing anumber of false images. Some experiments have been performed usingoptical phased arrays as emitters for various applications. Howeverprevious implementations, particularly those using fiber based delaylines, have been extremely expensive and cumbersome.

In the prior art, any related sweeping action, such as beam steering ofthe electromagnetic beam, has typically been accomplished by amechanical fixture of some sort. Sweeping a beam through a range ofangles is most commonly done today through mechanical gimbal assemblies,or through mechanically steered mirrors.

There is a need for an efficient and cost effective optical phased arraydevice.

SUMMARY OF THE INVENTION

According to one aspect, the invention relates to an integrated photonicbeam steering device. The integrated photonic beam steering devicecomprises a planar photonic substrate; an input waveguide disposed onthe planar photonic substrate and configured to accept electromagneticenergy from a source of electromagnetic energy radiation; a firstsplitter disposed on the planar photonic substrate and optically coupledto the input waveguide and configured to split the electromagneticradiation into one or more paths; and one or more phased array rowsdisposed on the planar photonic substrate and optically coupled to eachof the one or more paths. Each phased array row comprises a row splitterconfigured to split the each of the one or more paths into two or morerow paths; two or more phase modulators, each of the two or more phasemodulators optically coupled respectively via a row waveguide to each ofthe two or more row paths, each of the two or more phase modulatorshaving a phase modulator output. The device also includes two or moreoutput couplers optically coupled respectively to each phase modulatoroutput of the two or more phase modulators, each of the two or moreoutput couplers configured to emit electromagnetic radiation away fromthe substrate, the two or more output couplers configured to radiate asteered photonic beam away from the integrated photonic beam steeringdevice.

In one embodiment, at least one of the two or more output couplerscomprises a vertical coupler. In one embodiment, the vertical couplercomprises a grating coupler. In one embodiment, the grating couplercomprises a collection of curved trenches. In one embodiment, thegrating coupler comprises a collection of scattering sources. In oneembodiment, the vertical coupler comprises an etched facet. In oneembodiment, the vertical coupler comprises an etched angle. In oneembodiment, at least one of the two or more output couplers comprises anedge coupler. In one embodiment, the edge coupler comprises a cleavedand polished surface. In one embodiment, the edge coupler comprises ataper on an end of a waveguide.

In one embodiment, the invention provides a stacked integrated photonicbeam steering device comprising a plurality of the integrated photonicbeam steering devices and configured to emit an electromagnetic beamhaving phase coherent optical modes, the stacked integrated photonicbeam steering device is configured to provide a beam that is steerablein two orthogonal directions. In one embodiment, the two or more phasemodulators comprise a free carrier based integrated optical phasemodulator. In one embodiment, the two or more phase modulators comprisea nonlinear polymer integrated optical phase modulator. In oneembodiment, the steered photonic beam comprises at least one wavelengthin wavelength range of about 200 nm to 200 μm.

In one embodiment, the invention provides an electronic countermeasuresystem comprising the integrated photonic beam steering device, whereinthe steered photonic beam comprises an electronic countermeasure signal.In one embodiment, the electronic countermeasure signal is configured toconfuse a missile guidance system. In one embodiment, the electroniccountermeasure signal is configured to confuse a selected one ofdetection and surveillance system.

In one embodiment, the invention provides a integrated photonic beamsteering system that comprises a source of electromagnetic radiationhaving a wavelength range in a wavelength range of about 200 nm to 200μm; and an integrated photonic beam steering device coupled to thesource of electromagnetic radiation and configured to transmit a phasearrayed optical electromagnetic signal suitable for a selected one ofLIDAR and LADAR. In one embodiment, the integrated photonic beamsteering system further comprises a detector configured to receive areturn optical electromagnetic signal, configured to provide phasedetection, and configured to measure a delay between the transmittedphase arrayed optical electromagnetic signal and the received returnoptical electromagnetic signal. and a system output configured toprovide a measure of the delay. In one embodiment, the detector is phasesensitive. In one embodiment, the detector is disposed on the planarsubstrate.

The foregoing and other objects, aspects, features, and advantages ofthe invention will become more apparent from the following descriptionand from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of the invention can be better understood withreference to the drawings described below, and the claims. The drawingsare not necessarily to scale, emphasis instead generally being placedupon illustrating the principles of the invention. In the drawings, likenumerals are used to indicate like parts throughout the various views.

FIG. 1 is a diagram showing dispersion plots for the fundamental mode(Ex polarized) of exemplary clad and unclad waveguides, shown aseffective index vs. wavelength in μm.

FIG. 2 is a diagram showing an SEM image of an exemplary ring resonator.

FIG. 3 is a diagram showing the normalized transmission of light throughthe system (and past the ring) in dB, as a function of wavelengthdetuning in nm for both clad and unclad waveguides, shifted to overlayresonance peaks.

FIG. 4 is a diagram showing the device layout of an exemplary slotwaveguide.

FIG. 5 is a diagram showing the measured transmission spectrum in dB vs.laser wavelength in nm past a high quality factor slot ring resonator.

FIG. 6 is a diagram showing the detail of the peak of the transmissionspectrum near 1488 nm.

FIG. 7 is a diagram showing a shallow angle SEM view of a typicalsilicon-on-insulator ring resonator and waveguide having a sidewallroughness on the order of 10 nm.

FIG. 8 is a diagram of a slot ring resonator directional coupler region,and the associated input waveguide.

FIG. 9 is a diagram showing an exemplary high-index segmented waveguidestructures, which in the embodiment shown comprises a central waveguideportion with fingers or ridges sticking out to the sides.

FIG. 10A is a diagram that shows a dispersion diagram of both asegmented waveguide and the normal, unsegmented waveguide, taken on aplane parallel to the substrate that on a z plane intersects the middleof a segment.

FIG. 10B is a diagram that shows modal patterns of the Bloch mode, withcontours of |E| plotted, starting at 10% of the max value and withcontour increments of 10%.

FIG. 10C is a diagram that shows a plot of modal patterns over fourperiods of a segmented waveguide on a horizontal plane that intersectsthe silicon layer halfway through.

FIG. 11 is a diagram that shows an exemplary electrical isolator thatwas constructed and tested, and which provided both a transition from astandard to a slotted waveguide and electrical isolation between the twosides of the slot waveguide.

FIG. 12 is a four panel diagram that shows details of one embodiment ofan optical modulator device, including the geometry of thephotodetectors and filters, and including a cross section of the slottedwaveguide.

FIG. 13 shows a diagram of a Mach-Zehnder modulator with a conventionalelectrode geometry in top-down view, including top contact, waveguide,and bottom contact layers.

FIG. 14A shows the static voltage potential field distribution due tocharging the two electrodes.

FIG. 14B shows the electric field due to the potential distribution. |E|is plotted in increments of 10%.

FIG. 15A shows a cross section of the segmented, slotted waveguide, withthe |E| field plotted in increments of 10% of max value.

FIG. 15B shows a similar plot for the unsegmented waveguide.

FIG. 15C shows a horizontal cross section of the segmented, slottedwaveguide in which Re(Ex) is plotted in increments of 20% of max.

FIG. 16A is a diagram of the silicon slot waveguide used in theMach-Zehnder modulator, according to principles of the invention.

FIG. 16B is an SEM micrograph of a slot waveguide, according toprinciples of the invention.

FIG. 17A is a diagram of the modulator layout, according to principlesof the invention.

FIG. 17B and FIG. 17C are two SEM micrographs of modulators constructedaccording to principles of the invention, that show the slotted,segmented region, as well as the location where the silicon makescontact with the electrical layer.

FIG. 18 is a diagram that shows a transmission spectrum of an electrodedslot waveguide resonator with a gap of 70 nm. Fiber to fiber insertionloss is plotted in dB, against the test laser wavelength in nm.

FIG. 19 shows a diagram of a top view of one exemplary embodiment of aplanar integrated photonic circuit beam steering device.

FIG. 20 shows a side view of an integrated photonic beam steering deviceradiating a steered photonic beam.

FIG. 21 shows a diagram of a vertical coupling section of a gratingcoupler based beam steering array.

FIG. 22A shows a top and side view of an angle etched (etched angle)vertical scattering site.

FIG. 22B shows a top and side view of an etched facet verticalscattering site.

FIG. 23 shows a diagram of one embodiment of an exemplary single-layeredge coupled beam steerable device.

FIG. 24 shows a side view of one exemplary stack of edge coupled beamsteering chips.

DETAILED DESCRIPTION

We now describe high index contrast waveguides that are useful toconcentrate light in order to enhance nonlinear optical effects invarious materials so that such effects can be employed to manipulatelight (or more generally electromagnetic radiation) at low power levels,as compared to conventional systems and methods that employ nonlinearoptical materials. The manipulation of electromagnetic radiation orlight can be useful to provide a variety of components that performoperations on light such as rectification, modulation, filtering, andlogic operations in a manner analogous to the same operations which areprovided using electronic devices operating on electrical signals. Forexample, an input light wave to be processed is impressed onto thecomponent. The light wave has at least one parameter characterizing thelight wave, such as one of an intensity, a polarization, a frequency, awavelength, and a duration (e.g., a pulse length, or in the case ofcontinuous wave light, an effectively infinite duration). After theinput light wave is processed (or interacts with the waveguide and theclad nonlinear optical material adjacent to the waveguide when present),an output signal is observed. In a circumstance where the input signalhas been processed, the output signal has at least one parameter that isdifferent from at least one parameter characterizing the input lightwave, including possibly an electrical output signal when the inputlight wave had no electrical signal component (e.g., opticalrectification).

We have developed a set of tools for concentrating light to a highdegree by using silicon or other high index contrast waveguides, and wehave fabricated devices that demonstrate some of the many applicationsthat can be contemplated when such nonlinear materials are exploited. Inparticular, by utilizing split waveguides, we are able to greatlyenhance the optical fields in the cladding of a tightly confinedwaveguide, without greatly enhancing the optical losses of the samewaveguide. Combining the high field concentrations available from thesplit waveguides with the high nonlinear activity of nonlinear opticalpolymers permits the development of nonlinear optical devices operatingat much lower optical input power levels than are possible withconventional free space or chip based systems. We have demonstratedfour-wave mixing (which is based upon χ³), as well as opticalrectification (based on χ²), in such waveguides. Using these waveguidesit is possible to decrease the power levels needed to observesignificant nonlinearities to the point where, by contrast withconventional nonlinear optics, it can be done with non-pulsed,continuous wave lasers.

Chi2 (χ²) and Chi3 (χ³) based optical effects can be used in particularto build on-chip optical parametric oscillator (“OPO”) systems, wheretwo input wavelengths can be mixed together to produce sum anddifference frequencies. These frequencies can be either higher or lowerthan the input frequencies, and can be made tunable. These effects workfor frequencies from the ultraviolet and X-ray regime all the way outinto the far infrared and microwave, and in fact can work down to DC insome cases, particularly with optical rectification.

The material of which the high index waveguide is made can be anymaterial having a high index that is reasonably transparent at thewavelengths of interest. This can include but is not limited to silicon,gallium nitride, indium phosphide, indium gallium nitride, galliumphosphide, diamond, sapphire, or the various quaternary III/V and II/VImaterials such as aluminum gallium arsenide phosphide. III/V denotesmaterials having at least one element from column III of the periodictable of elements (or an element that is stable as a positive trivalention) and at least one element from column V (or an element that isstable as a negative trivalent ion). Examples of III/V compounds includeBN, ALP, GaAs and InP. II/VI denotes materials having at least oneelement from column II of the periodic table of elements (or an elementthat is stable as a positive divalent ion) and at least one element fromcolumn VI (or an element that is stable as a negative divalent ion).Examples of II/VI compounds include MgO, CdS, ZnSe and HgTe.

We present successively the mechanical structure of exemplaryembodiments of high index waveguides, exemplary embodiments of claddingmaterials having large nonlinear constants χ² and χ³ and theirincorporation into devices having high index waveguides, and someexemplary results observed on some of the fabricated devices that aredescribed.

Exemplary High Index Waveguide Structures High-Q Ring Resonators in ThinSilicon-on-Insulator

Resonators comprising high-Q microrings were fabricated from thinsilicon-on-insulator (SOI) layers. Measured Q values of 45,000 wereobserved in these rings, which were then improved to 57,000 by adding aPMMA cladding. Various waveguide designs were calculated, and thewaveguide losses were analyzed.

Microring resonator structures as laser sources and as optical filterelements for dense wavelength division multiplexing systems have beenstudied in the past. The silicon-on-insulator (SOI) structure describedhere is particularly advantageous. It has low waveguide loss. One canextrapolate an uncoupled Q value of 94,000 and a waveguide loss of 7.1dB/cm in the unclad case, and −6.6 dB/cm in the PMMA clad case, from therespective measured Q values of 45,000 and 57,000. Although higher Qvalues have been obtained for optical microcavities, we believe that ourgeometry has the highest Q for a resonator based on a single modesilicon waveguide. It is also noteworthy that a large amount of powerappears outside the core silicon waveguide, which may be important insome applications. The modes that are described herein haveapproximately 57% of the power outside the waveguide, as compared to 20%for a single-mode 200-nm-thick silicon waveguide, and 10% for asingle-mode 300-nm-thick silicon waveguide.

In one embodiment, wafer geometries were selected that minimize thethickness of the SOI waveguiding layer as well as the buried oxide, butstill yield low loss waveguides and bends. A number of differentwaveguide widths were compared by finite difference based mode solving.The geometry used in the exemplary embodiment comprises a 500-nm-widewaveguide formed in a 120-nm-thick silicon layer, atop a 1.4 μm oxidelayer, which rests on a silicon handle, such as a silicon wafer as asubstrate. Such a configuration supports only a single well-containedoptical mode for near infrared wavelengths. The dispersioncharacteristics are shown in FIG. 1 for both unclad and PMMA-cladwaveguides. Our interest in unclad structures stems from the ease offabrication, as detailed in the following, as well as the flexibility anopen air waveguide may provide for certain applications.

These modes were determined by using a finite difference based Hermitianeigensolver. It is possible to calculate the loss directly from the modepattern with an analytic method valid in the low-loss limit. Thewaveguide loss at 1.55 μm calculated in such a fashion is approximately−4.5 dB. This loss figure was in agreement with the extrapolated resultsof FDTD simulation.

Because a loss of −4 dB/cm is attributed to substrate leakage, thewaveguide loss can be improved by the addition of a cladding, whichtends to pull the mode upwards. This notion is supported by the measureddecrease in waveguide loss upon the addition of a PMMA cladding. It canbe shown that the substrate leakage loss attenuation coefficient isnearly proportional to

e⁻²√{square root over (n_(eff) ²−n_(o) ²)}k₀A

if k₀ is the free space wave number, n_(eff) is the effective index ofthe mode, n_(o) is the effective index of the oxide layer, and A is thethickness of the oxide. In the present case, the e-folding depth of theabove-mentioned function turns out to be 180 nm, which explains why thesubstrate leakage is so high.

SOI material with a top silicon layer of approximately 120 nm and 1.4 μmbottom oxide was obtained in the form of 200 mm wafers, which weremanually cleaved, and dehydrated for 5 min at 180° C. The wafers werethen cleaned with a spin/rinse process in acetone and isopropanol, andair dried. HSQ electron beam resist from Dow Corning Corporation wasspin coated at 1000 rpm and baked for 4 min at 180° C. The coatedsamples were exposed with a Leica EBPG-5000+ electron beam writer at 100kV. The devices were exposed at a dose of 4000 μc/cm², and the sampleswere developed in MIF-300 TMAH developer and rinsed with water andisopropanol. The patterned SOI devices were subsequently etched by usingan Oxford Plasmalab 100 ICP-RIE within 12 mTorr of chlorine, with 800 Wof ICP power and 50 W of forward power applied for 33 s. Microfabricateddevices such as the one shown in FIG. 2 were tested by mounting the diesonto an optical stage system with a single-mode optical fiber array. Atunable laser was used first to align each device, and then swept inorder to determine the frequency domain behavior of each of the devices.Light was coupled into the waveguides from a fiber mode by the use ofgrating couplers. Subsequently the devices were spin-coated with 11% 950K PMMA in Anisole, at 2000 rpm, baked for 20 min at 180° C., andretested.

The theoretical development of the expected behavior of a ring resonatorsystem has been described in the technical literature. In the presentcase the dispersion of the waveguide compels the addition of adispersive term to the peak width. We take λ₀ to be the free spacewavelength of a resonance frequency of the system, n₀ to be the index ofrefraction at this wavelength, (δn/δλ)₀, the derivative of n withrespect to λ taken at λ₀, L to be the optical path length around thering, α to be the optical amplitude attenuation factor due to loss in asingle trip around the ring, and finally t to be the optical amplitudeattenuation factor due to traveling past the coupling region. In thelimit of a high Q, and thus (1−α)<<1 and (1−t)<<1,

we have

Q=(πL/λ ₀)[n ₀−λ₀(δn/δλ)₀]/(1−αt)  (1)

The waveguide mode was coupled into a ring resonator from an adjacentwaveguide. As shown in FIG. 2, the adjacent waveguide can in someembodiments be a linear waveguide. The strength of coupling can then belithographically controlled by adjusting the distance between thewaveguide and the ring. This ring was fabricated with a radius of 30 μm,a waveguide width of 500 nm, and a separation between ring and waveguideof 330 nm. For the clad ring presented, the measured Q is 45,000, andthe extinction ratio is −22 dB, for the resonance peak at 1512.56 nm.The PMMA clad ring had a similar geometry, and achieved a Q of 57,000,but with an extinction ratio of −15.5 dB. Typical observed transmissionspectra are shown in FIG. 3. The typical amount of optical power in thewaveguide directly coupling into the resonator was about 0.03 mW. Adependence of the spectrum on this power was not observed, to within anorder of magnitude.

From the mode-solving results for the unclad waveguides, we have(δn/δλ)(1.512)=−1.182 μm⁻¹, and n(λ=1.512)=1.688. Using this result andthe earlier relations, the waveguide loss can be calculated from themeasured Q value. Specifically, an extinction that is at least −22 dBindicates that a critically coupled Q in this geometry is greater than38,500, which then implies a waveguide loss of less than −7.1 dB/cm. Insimilar fashion, the PMMA clad waveguide resonator with a Q of 57,000but only −15.5 dB of extinction allows a worst case waveguide loss of−6.6 dB/cm. This also implies an intrinsic Q of 77,000 for the uncladresonator, and an intrinsic Q of 94,000 for the PMMA clad resonator.

These devices have a slight temperature dependence. Specifically, theresonance peak shifts correspondingly with the change in the refractiveindex of silicon with temperature, moving over 2 nm as temperatureshifts from 18 to 65° C. The Q rises with higher temperatures slightly,from 33 k at 18° C. to 37 k on one device studied. This shift canprobably be explained entirely by the dependence of Q on the effectiveindex.

High-Q Optical Resonators in Silicon-on-Insulator Based Slot Waveguides

We now describe the design, fabrication and characterization of high Qoval resonators based on slot waveguide geometries in thin silicon oninsulator material. Optical quality factors of up to 27,000 weremeasured in such filters, and we estimate losses of −10 dB/cm in theslotted waveguides on the basis of our resonator measurements. Suchwaveguides enable the concentration of light to very high optical fieldswithin nano-scale dimensions, and show promise for the confinement oflight in low-index material with potential applications for opticalmodulation, nonlinear optics and optical sensing. As will beappreciated, the precise geometry of a resonator (or other kinds ofdevices) is frequently a matter of design, and the geometry can bevaried based on such considerations as length of waveguide, area of achip, and required interaction (or required non-interaction), such ascoupling (or avoiding coupling) with other waveguide structures that arepresent in a device or on a chip. In some embodiments, the waveguide canbe a closed loop, such as at least one ring or at least one oval shapedendless stripe. As has been explained, optical energy can be provided tosuch a closed loop, for example with an input waveguide.

One can form high quality factor ring or oval resonators in SOI. Inthese SOI waveguides, vertical confinement of light is obtained from theindex contrast between the silicon core and the low index cladding (orair) and the buried silicon dioxide layer, whereas lateral confinementcan be obtained by lithographically patterning the silicon. The majorityof the light tends to be guided within the silicon core in suchwaveguide. Although the high refractive index contrast between siliconand its oxide provide excellent optical confinement, guiding within thesilicon core can be problematic for some applications. In particular, atvery high optical intensities, two-photon absorption in the silicon maylead to high optical losses. Moreover, it is often desirable to maximizethe field intensity overlap between the optical waveguide mode and alower index cladding material when that cladding is optically active andprovides electro-optic modulation or chemical sensing.

One solution to these problems involves using a slot waveguide geometry.In a slot waveguide, two silicon stripes are formed by etching an SOIslab, and are separated by a small distance. In one embodiment, theseparation is approximately 60 nm. The optical mode in such a structuretends to propagate mainly within the center of the waveguide. In thecase of primarily horizontal polarization, the discontinuity conditionat the cladding-silicon interface leads to a large concentration of theoptical field in the slot or trench between the two stripes. One canpredict that the electric field intensity would be approximately 10⁸ √PV/m where P is the input power in watts. One design uses a 120 nmsilicon on insulator layer and 300 nm wide silicon strips on top of a1.4 μm thick buried oxide layer, which is in turn deposited on a siliconsubstrate. Various widths for the central slot were fabricated toprovide test devices with 50, 60 and 70 nm gaps. Slots larger than 70 nmhave also been fabricated and were shown to work well.

In the 1.4-1.6 μm wavelength regime, the waveguide geometry is singlemode, and a well-contained optical mode is supported between the twosilicon waveguide slabs. There is some loss that such an optical modewill experience even in the absence of any scattering loss or materialabsorption due to leakage of light into the silicon substrate. Thesubstrate loss can be estimated semi-analytically via perturbationtheory, and ranges from approximately −0.15 dB/cm at 1.49 μm to about−0.6 dB/cm at 1.55 μm for the SOI wafer geometry of the presentembodiment.

Oval resonators were fabricated by patterning the slot waveguides intoan oval shape. An oval resonator geometry was selected in preference tothe more conventional circular shape to enable a longer couplingdistance between the oval and the external coupling waveguide or inputwaveguide. See FIG. 4. Slots were introduced into both the oval andexternal coupling waveguides.

Predicting coupling strength and waveguide losses for such devices isnot easy. Many different coupling lengths and ring to input waveguideseparations were fabricated and tested. It is well known that the mostdistinct resonance behavior would be observed for critically coupledresonators, in which the coupling strength roughly matches the roundtrip loss in the ring.

An analytic expression for the quality factor of a ring resonator waspresented in equation (1) hereinabove.

Also, the free spectral range can be calculated via:

Δλ=(λ₀ /L)/[1/L+n ₀/λ₀−(δn/δλ)₀]  (2)

Here, L is the round trip length in the ring, and n₀ and λ₀ are theindex of refraction, and the wavelength at resonance, respectively. Thederivative of the effective index with respect to the wavelength at theresonance peak is given by (δn/δλ)₀, and it can be shown that this termis roughly equal to −0.6 μm⁻¹ from the 1.4-1.6 μm spectral range for theslot waveguides studied here.

We have observed a quality factor of 27,000 in a device fabricated witha slot size of 70 nm, a ring to input waveguide edge to edge separationof 650 nm, and a coupling distance of 1.6 μm. The radius of the circularpart of the slotted oval was 50 μm. This resonance was observed near1488 nm, and the resonance peak had an extinction ratio of 4.5 dB. FIG.5 shows the measured transmission spectrum past the ring, normalized forthe input coupler baseline efficiency of our test system. FIG. 6 showsthe details of one peak in the vicinity of 1488 nm. Because theextinction ratio at the resonance peak was not very large in this case,it was not possible to accurately determine waveguide losses from thisdevice. By measuring many devices with different geometries, we obtaineddata on resonators with higher extinction ratios that approachedcritical coupling. One such device was a 50 μm radius slotted ringresonator with a 60 nm waveguide gap, a ring to input waveguide spacingof 550 nm and coupling length of 1.6 μm. In this device, a Q of 23,400was observed near 1523 nm, with an on-resonance extinction of 14.7 dB.

Since this resonance is nearly critically coupled, the waveguide losscan be estimated using equation (1) as −10 dB/cm. We can also useequation (2) to further validate our theoretical picture of the ringresonator. The observed free spectral range of this resonator was 2.74nm, while equation (2) predicts 2.9 nm. This discrepancy is most likelydue to small differences in the fabricated dimensions as compared tothose for which the numerical solutions were obtained.

To further validate the waveguide loss result, several waveguide losscalibration loops were fabricated with varying lengths of the slotwaveguide, ranging from 200 to 8200 um in length. A total of five centerslot waveguide devices were studied for each of the 50, 60 and 70 nmslot widths. Linear regression analysis on the peak transmission of eachseries yielded waveguide loss figures of 11.6±3.5 dB/cm for the 50 nmcenter waveguide, 7.7±2.3 dB/cm for the 60 nm center waveguide, and8.1±1.1 dB/cm for the 70 nm center waveguide. These figures are inagreement with the loss estimated from the oval resonator. Since thetheoretical loss due to substrate leakage is much lower than this, it isclear that a great deal of loss is due to surface roughness and possiblymaterial absorption. It is believed that engineering improvements willdecrease this loss further. For sensing and modulation applications aswell as use in nonlinear optics, the high optical field concentrationthat can be supported in the cladding material of the slotted waveguidegeometry should be very advantageous when compared to more conventionalwaveguides.

FIG. 7 is a diagram showing a shallow angle SEM view of asilicon-on-insulator ring resonator and waveguide having a sidewallroughness on the order of 10 nm. In the exemplary waveguide shown inFIG. 7, the silicon-insulator bond has been decorated with a briefbuffered oxide etch. FIG. 8 is a diagram of a slot ring resonatordirectional coupler region, and the associated input waveguide.

Other variations on the geometry of waveguides are possible. FIG. 9 is adiagram showing an exemplary high-index segmented waveguide structures,which in the embodiment shown comprises a central waveguide portion withfingers or ridges sticking out to the sides. With the light localized inthe center in a Bloch mode, electrical contact can be established usingthe fingers or ridges that stick off the sides of the waveguide. Thisstructure provides a way to form both electrical contacts to waveguidesand structures that would provide electrical isolation with low opticalloss. Through an iterative process involving a combination of opticaldesign using a Hermetian Bloch mode eigensolver and fabrication ofactual structures, it was found that (non-slotted) segmented waveguidestructures could be constructed in 120 nm thick SOI. Waveguide losses assmall as −16 dB per centimeter were observed, and insertion losses assmall as −0.16 dB were shown from standard silicon waveguides.

The segmented waveguide structure can also be modeled as regards itsexpected properties, which can then be compared to actual results. FIG.10A is a diagram that shows a dispersion diagram of both a segmentedwaveguide and the normal, unsegmented waveguide, taken on a planeparallel to the substrate that on a z plane that intersects the middleof a segment. FIG. 10B is a diagram that shows modal patterns of theBloch mode, with contours of |E| plotted, starting at 10% of the maxvalue and with contour increments of 10%. FIG. 10C is a diagram thatshows a plot of modal patterns over four periods of a segmentedwaveguide on a horizontal plane that intersects the silicon layerhalfway through.

By utilizing the same type of design methodology as was used for thesegmented waveguides, one is able to able to construct structures thatprovide electrical isolation without substantial optical loss. FIG. 11is a diagram that shows an exemplary electrical isolator that wasconstructed and tested, and which provided both a transition from astandard to a slotted waveguide and electrical isolation between the twosides of the slot waveguide. Such structures were shown to have losseson the order of 0.5 dB.

Optical Modulation and Detection in Slotted Silicon Waveguides

In this example, we describe a system and process that provide low poweroptical detection and modulation in a slotted waveguide geometry filledwith nonlinear electro-optic polymers and present examples thatdemonstrate such methods. The nanoscale confinement of the optical mode,combined with its close proximity to electrical contacts, enables thedirect conversion of optical energy to electrical energy, withoutexternal bias, via optical rectification, and also enhanceselectro-optic modulation. We demonstrate this process for power levelsin the sub-milliwatt regime, as compared to the kilowatt regime in whichoptical nonlinear effects are typically observed at short length scales.The results presented show that a new class of detectors based onnonlinear optics can be fabricated and operated.

Waveguide-based integrated optics in silicon provide systems and methodsfor concentrating and guiding light at the nanoscale. The high indexcontrast between silicon and common cladding materials enables extremelycompact waveguides with very high mode field concentrations, and allowsthe use of established CMOS fabrication techniques to define photonicintegrated circuits. By using slotted waveguides, it is possible tofurther concentrate a large fraction of the guided mode into a gapwithin the center of a silicon waveguide. This geometry greatlymagnifies the electric field associated with the optical mode, resultingin electric fields of at least (or in excess of) 10 ⁶ V/m forcontinuous-wave, sub-milliwatt optical signals. Moreover, since theslotted geometry comprises two silicon strips which can be electricallyisolated, a convenient mechanism for electro-optic interaction isprovided. Such waveguides can be fabricated with low loss. We havepreviously described systems that provide losses below −10 dB/cm.

In the present example, we exploit both the high intensity of theoptical field and the close proximity of the electrodes for severalpurposes. First, we demonstrate detection of optical signals via directconversion to electrical energy by means of nonlinear opticalrectification. An exemplary device comprises a ring resonator with anelectro-optic polymer based χ² material deposited as a cladding. Insidethe slot, the high optical field intensity creates a standing DC field,which creates a virtual voltage source between the two siliconelectrodes, resulting in a measurable current flow, in the absence ofany external electrical bias. Though optical rectification has beenobserved in electro-optic polymers, typically instantaneous opticalpowers on the order of 1 kW are needed for observable conversionefficiencies, often achieved with pulsed lasers. The exemplaryembodiment provides measurable conversion with less than 1 mW ofnon-pulsed input, obtained from a standard, low power tunable laseroperating near 1500 nm.

In one embodiment, systems and methods of the invention provide standardPockels' effect based modulation, which is similarly enhanced by meansof the very small scale of our device. The close proximity of theelectrodes, and ready overlap with the optical mode, causes an externalvoltage to produce a far larger effective electric modulation field, andtherefore refractive index shift, than would be obtained throughconventional waveguide designs. In one embodiment, the modulation andrefractive index shift is provided by tuning the resonance frequenciesof a slot waveguide ring resonator.

Device Fabrication Waveguide Fabrication

The devices described in this example were fabricated in electronicgrade silicon-on-insulator (SOI) with a top layer thickness of 110 nmand an oxide thickness of 1.3 microns. The silicon layer is subsequentlydoped to approximately 10¹⁹ Phosphorous atoms/cm³, yieldingresistivities after dopant activation of about 0.025 ohm-cm.Electro-optic (“EO”) polymers were then spin-deposited onto thewaveguide structures and subsequently poled by using a high fieldapplied across the slot in the waveguide.

Lithography was performed using a Leica EBPG 5000+ electron beam systemat 100 kv. Prior to lithography, the samples were manually cleaved,cleaned in acetone and isopropanol, baked for 20 minutes at 180 C,coated with 2 percent HSQ resist from Dow Corning Corporation, spun fortwo minutes at 1000 rpm, and baked for an additional 20 minutes. Thesamples were exposed at 5 nm step size, at 3500 μC/cm². The samples weredeveloped in AZ 300 TMAH developer for 3 minutes, and etched on anOxford Instruments PLC Plasmalab 100 with chlorine at 80 sccm, forwardpower at 50 W, ICP power at 800 W, 12 mTorr pressure, and 33 seconds ofetch time. The samples were then implanted with phosphorous at normalincidence, 3 OkeV energy, and 1×10¹⁴ ions/cm² density. The sample wasannealed under a vacuum at 950 C in a Jipilec Jetstar rapid thermalannealer. The samples were dipped in buffered hydrofluoric acid in orderto remove the remnants of electron beam resist from the surface.

After initial optical testing, the samples were coated with YLD 124electro-optic polymer, and in one case with dendrimer-basedelectro-optic material. The samples were stored under a vacuum at alltimes when they were not being tested, in order to reduce the chances ofany degradation.

Measurement Results Optical Rectification Based Detection

FIG. 12 is a four panel diagram that shows details of one embodiment ofan optical modulator device, including the geometry of thephotodetectors and filters, and including a cross section of the slottedwaveguide. Panel A of FIG. 12 shows a cross section of the devicegeometry with optical mode superimposed on a waveguide. In FIG. 12A, theoptical mode was solved using a finite-difference based HermetianEigensolver, such as that described by A. Taflove, ComputationalElectrodynamics, (Artech House, Boston. MA, 1995), and has an effectiveindex of approximately 1.85 at 1500 nm. Most of the electric field isparallel to the plane of the chip, and it is possible to contact bothsides of the slot in a slotted ring resonator, as shown in FIG. 12B,which shows a SEM image of the resonator electrical contacts.Electrically isolated contacts between the silicon rails defining theslotted waveguide introduce only about 0.1 dB of optical loss. FIG. 12Cshows the logical layout of device, superimposed on a SEM image of adevice. FIG. 12C details the layout of a complete slotted ringresonator, with two contact pads connected to the outer half of thering, and two pads electrically connected to the inner half of the ring.A shunt resistor provides a means of confirming electrical contact, andtypical pad-to-pad and pad-to-ring resistances range from 1 MΩ to 5 MΩ.FIG. 12D displays a typical electrically contacted slotted ring aspresently described. FIG. 12D is an image of the ring and the electricalcontact structures.

Measurements were performed with single-mode polarization maintaininginput and output fibers, grating coupled to slotted waveguides with aninsertion loss of approximately 8 dB. Optical signal was provided froman Agilent 81680A tunable laser and in some cases an erbium doped fiberamplifier (“EDFA”) from Keopsys Corporation. A continuous optical signalinserted into a poled polymer ring results in a measurable currentestablished between the two pads, which are electrically connectedthrough a pica-Ammeter. In the most sensitive device, a DC current of˜1.3 nA was observed, indicating an electrical output power of ˜10⁻⁹ ofthe optical input power (5×10⁻¹² W of output for approximately 0.5 mWcoupled into the chip). Control devices, in which PMMA or un-poled EOmaterial was substituted, show no photocurrent.

The fact that there is no external bias (or indeed any energy source)other than the optical signal applied to the system of this embodimentdemonstrates conclusively that power is being converted from the opticalsignal. To establish that the conversion mechanism is actually opticalrectification, we performed a number of additional measurements. Asteady bias was applied to the chip for several minutes, as shown inTable 1A. A substantial change in the photoresponse of the device wasobserved. This change depends on the polarity of the bias voltage,consistent with the expected influence of repoling of the devicein-place at room temperature. Specifically, if the external bias wasapplied opposing the original poling direction, conversion efficiencygenerally decreased, while an external bias in the direction of theoriginal poling field increased conversion efficiency.

TABLE 1 Polling Results Part A: Action New Steady State Current (6 dBminput) Initial State −5.7 pA +10 V for 2 minutes 0 pA −10 V for 2minutes −7.1 pA +10 V for 2 minutes −4.4 pA +10 V for 4 minutes −6.1 pA−10 V for 4 minutes −4.5 pA −10 V for 2 minutes −14.8 pA Part B: CurrentPolarity of Device Action Optical Rectification 1 Positive PolingPositive 1 Thermal Cycling to Rapid fluctuation, did poling temperaturewith not settle no voltage 1 Negative Poling Negative 2 Negative PolingNegative 2 Thermal Cycling to None observable Poling temperature with novoltage 2 Positive Poling Negative 3 Negative Poling Negative 4 PositivePoling Positive 5 Negative Poling Negative

To further understand the photo-conversion mechanism, 5 EO detectiondevices were poled with both positive and negative polarities, thusreversing the direction of the relative χ² tensors. For these materials,the direction of χ² is known to align with the polling E fielddirection, and we have verified this through Pockels' effectmeasurements. In all but one case, we observe that the polarity of thegenerated potential is the same as that used in poling, and the +Vterminal during poling acts as the −V terminal in spontaneous currentgeneration, as shown in Table 1B. Furthermore, the polarity of thecurrent is consistent with a virtual voltage source induced throughoptical rectification. It was observed that these devices decaysignificantly over the course of testing, and that in one case thepolarity of the output current was even observed to spontaneously switchafter extensive testing. However, the initial behavior of the devicesafter polling seems largely correlated to the χ² direction.

Part A of Table 1 shows the dependence of the steady state observedcurrent after room temperature biasing with various voltage polaritiesfor one device. The device was originally polled with a ˜12 V bias,though at 110 C. With one exception, applying a voltage in the directionof the original polling voltage enhances current conversionefficiencies, while applying a voltage against the direction of thepolling voltage reduces the current conversion efficiencies. It shouldbe noted that the power coupled on-chip in these measurements was lessthan 1 mW due to coupler loss.

Part B of Table 1 shows the behavior of several different devicesimmediately after thermal polling or cycling without voltage.Measurements were taken sequentially from top to bottom for a givendevice. The only anomaly is the third measurement on device 2; this wasafter significant testing, and the current observed was substantiallyless than was observed in previous tests on the same device. We suspectthat the polymer was degraded by repeated testing in this case.

Analysis of Data for Optical Rectification

To derive the magnitude of the expected photocurrent, we assume that theχ² magnitude relating to the Pockels' effect is similar to that foroptical rectification. A measurement of χ² can then be obtained from thedirect observation of the electro-optic coefficient by the standardmeasurements described earlier. The typical measured tuning value of 2GHzN yields approximately 50 μm/V.

In the best case, devices with 6 dBm of input power returnedapproximately 1.4 nA of current. With Qs ranging from 3 k to 5 k, andassuming approximately 7 dB of insertion loss in the input gratingcoupler on one of our chips, in the best case as much as 0 dBm might becirculating in a resonator on resonance. This implies a peak electricfield due to the optical signal of approximately 3.1×10⁶ V/m. Theinduced static nonlinear polarization field is then nearly 1000 V/m,which amounts to a voltage drop of 14×10^(˜5) V across a 140 nm gap. Ifthis voltage is assumed to be perfectly maintained, and the loadresistance is assumed to be 5 MΩ, then 28 pA would be generated, about afactor of 100 less than is observed in the largest measurement made, butwithin a factor of 20 of the typical measurement of 352 pA for 6 dBm ofinput. Significantly, because the generated current is quadratic in E,it is clear that the current will be linearly proportional to the inputintensity. This is in accordance with our observations. The best resultsfor optical rectification were obtained with YLD 124/APC polymer,whereas our best Pockels' Effect results were obtained with thedendrimer materials.

Significantly, the sign of the output current matches that which wouldbe predicted by nonlinear optical rectification, as discussed above.Specifically, since positive current emanates from the positiveterminal, the rectified E field has a sign reversed from the χ² and thepolling E field. It is well established that the χ² direction tends toalign with the direction of the polling E field. Because of this, therectified field acting as a voltage source will produce an effectivepositive terminal at the terminal that had the positive polling voltage.

We do not yet fully understand the current generation mechanism. Inparticular, it is not clear what provides the mechanism for chargetransport across the gap. The APC material in which the nonlinearpolymer is hosted is insulating, and though it does exhibit thephotoconductivity effect due to visible light, it is unclear whether itcan for near-infrared radiation. Photoconductivity due to secondharmonic generation may play a role in this effect. It is certainly thecase, however, that current flows through this gap; that is the onlyregion in the entire system where an electromotive force exists. Also,photoconductivity alone is not adequate to explain the reversal of thecurrent coming from the detector devices when the poling direction isreversed, nor the conversion of the optical input into directed currentin general. The only mechanism to our knowledge that adequately explainsthis data is optical rectification.

If we assume that it will be possible to achieve a 10-fold improvementin the Q's of the resonators, while still getting more than 10 dB ofextinction, then the intensity circulating in such a ring would be about13 dB up from the intensity of the input wave. By comparison, with a Qof about 1000 and high extinction, the peak circulating intensity isabout the same as the intensity in the input waveguide. Therefore, it isreasonable to expect that it will be possible to get at least 10 dB ofimprovement in the circulating intensity, and thus in the conversionefficiency, by fabricating higher Q rings.

By combining the nano-scale slotted waveguide geometry withelectro-optical polymers having high nonlinear constants, we haveobtained massive enhancement of the optical field. That has in turnenabled us to exploit nonlinear optical processes that are typicallyonly available in the kW regime in the sub-mW regime. This difference isso considerable that we believe it represents a change in kind for thefunction of nonlinear optical devices. In addition, it is believed thatthis hybrid material system provides systems and methods for creatingcompact devices that exploit other nonlinear phenomena on-chip.

Optical rectification based detectors can have many advantages overcurrently available technology. In particular, such detectors areexpected to function at a higher intrinsic rate than the typicalphotodiode in use, as the optical rectification process occurs at theoptical frequency itself, on the order of 100 THz in WDM systems. Theabsence of an external bias, and the generation of a voltage rather thana change in current flow, both provide certain advantages in electronicoperation. We also believe that a device based on nonlinear opticalrectification will not suffer from the limitation of a dark current.This in turn can provide WDM systems that will function with loweroptical power, providing numerous benefits. Similarly, our demonstrationof enhanced modulation using these waveguide geometries provides usefulcomponents for future communications systems.

We believe that there will be advantageous economic aspects of suchdevices in various embodiments. Because our devices can be fabricated inplanar electronics grade silicon-on-insulator, using processescompatible with advanced CMOS processing, it is expected that devicesembodying these principles will be less expensive to fabricate.

Optical Modulators

Optical modulators are a fundamental component of optical datatransmission systems. They are used to convert electrical voltage intoamplitude modulation of an optical carrier frequency, and they can serveas the gateway from the electrical to the optical domain. High-bandwidthoptical signals can be transmitted through optical fibers with low lossand low latency. All practical high-speed modulators that are in usetoday require input voltage shifts on the order of 1V to obtain fullextinction. However it is extremely advantageous in terms of noiseperformance for modulators to operate at lower drive voltages. Manysensors and antennas generate only millivolts or less. As a result it isoften necessary to include an amplifier in conventional opticaltransmission systems, which often limits system performance. By usingsilicon nano-slot waveguide designs and optical polymers, it is possibletoday to construct millivolt-scale, broadband modulators. In someembodiments, a millivolt-scale signal is one having a magnitude in therange of hundreds of millivolts down to units of millivolts. Using novelnanostructured waveguide designs, we have demonstrated a 100×improvement in Vπ over conventional electro-optic polymer modulators.

A variety of physical effects are available to produce opticalmodulation, including the acousto-optic effect, the Pockels effecteither in hard materials, such as lithium niobate or in electro-opticpolymers, free-carrier or plasma effects, electro-absorption, andthermal modulation. For many types of optical modulation, the basicdesign of a modulator is similar; a region of waveguide on one arm of aMach-Zehnder interferometer is made to include an active opticalmaterial that changes index in response to an external signal. Thismight be, for instance, a waveguide of lithium niobate, or asemiconductor waveguide in silicon. In both cases, a voltage isintroduced to the waveguide region by means of external electrodes. Thiscauses the active region to shift in index slightly, causing a phasedelay on the light traveling down one arm of the modulator. When thelight in that arm is recombined with light that traveled down areference arm, the phase difference between the two signals causes thecombined signal to change in amplitude, with this change depending onthe amount of phase delay induced on the phase modulation arm. Otherschemes, where both arms are modulated in order to improve performance,are also common.

The measure of the strength of a modulation effect is how much phaseshift is obtained for a given input voltage. Typical conventionalmodulators obtain effective index shifts on the order of 0.004% for 1 V.This implies that a Mach-Zehnder 1 cm in length, meant to modulateradiation near 1550 nm, would require 1 V of external input for the armsto accumulate a relative phase shift of radians. The half wave voltageV_(π) (or V_(pi)) is the voltage needed for an interarm phase shift of πradians (or 180 degrees). Lower values for V_(π) imply that less poweris needed to operate the modulator. Often, the responsivity, alength-independent product V_(π)-L is reported. Typical V_(π)-L valuesare in the range of 8 Vcm in silicon, or 6 V-cm for lithium niobatemodulators. This voltage-length product, or responsivity, is animportant figure of merit for examining a novel modulator design. Makinga modulator physically longer generally trades lower halfwave voltageagainst reduced operating frequency and higher loss. Because generatinghigh-speed and high-power signals requires specialized amplifiers,particularly if broadband performance is required, lowering theoperating voltage of modulators is extremely desirable, particularly foron-chip integrated electronic/photonic applications, (includingchip-to-chip interconnects) where on-chip voltages are limited to levelsavailable in CMOS. FIG. 13 shows a diagram of a Mach-Zehnder modulatorwith a conventional electrode geometry.

FIG. 13 is a top-down view of a simple conventional Mach-Zehnder polymerinterferometer, showing top contact, waveguide, and bottom contactlayers. Such a device is usually operated in ‘push/pull’ mode, whereeither opposite voltages are applied to the different arms, or where thetwo arms are poled in opposite directions to achieve the same effect.

In the past several years, silicon has gained attention as an idealoptical material for integrated optics, in particular attelecommunications wavelengths. Low loss optical devices have beenbuilt, and modulation obtained through free carrier effects. One of thewaveguides that can be supported by silicon is the so-called slotwaveguide geometry. This involves two ridges of silicon placed close toeach other, with a small gap between them. We have demonstratedmodulation regions based on filling this gap with a nonlinear material,and using the two waveguide halves as electrodes. In such a geometry,the silicon is doped to a level that allows electrical conductivitywithout causing substantial optical losses. This allows the two wires orridges to serve both as transparent electrical contacts and as anoptical waveguide.

Using slot waveguides, we previously obtained an improvement inmodulation strength of nearly 5× when compared to the best contemporaryconventional waveguide geometries with electrodes separated from thewaveguide, with the initial, non-optimized designs. This improvement wasbased on the remarkably small width of the gap across which the drivingvoltage drops. It is expected that smaller gaps translate into higherfield per Volt, and the Pockels Effect depends on the local strength ofthe electric field. The smaller the gap, the larger the index shift. Aunique property of slot waveguides is that, even as these gaps becomenanoscale, the divergence conditions on the electric field require thatmuch of the optical mode remains within the central gap. As a result,changing the index within a nanoscale gap can give a remarkably largechange in the waveguide effective index. Because of these divergenceconditions, the optical mode's effective index is largely determined bythe shift found even in very small gaps.

Low V_(π) Modulators

Several major approaches toward achieving low V_(π) modulation haverecently been pursued. The free-carrier dispersion effect in siliconwaveguides has been used. Green et al. achieved a V_(π) of 1.8 V withthis effect. Modulators based on lithium niobate are also frequentlyused. Typical commercially obtained V_(π) values are 4 V. Recently,Mathine and co-workers have demonstrated a nonlinear polymer basedmodulator with a V_(π) of 0.65 V. For the devices produced by others,the attained values of V_(π) are large.

A number of approaches have been proposed for developing low V_(π)modulators. Different proposed approaches rely the development of newelectrooptic materials, or on optical designs that trade bandwidth forsensitivity, either through the use of resonant enhancement, or throughdispersion engineering. The designs presented herein are based uponconventional, high-bandwidth Mach-Zehnder traveling wave approaches, butachieve appreciable benefits from using nano-slot waveguides. Of course,these designs can also take advantage of the newest and bestelectrooptic polymers. In principle, any material that can be coatedconformally onto the surface of the silicon waveguides and that isreasonably resistive could be used to provide modulation in thesesystems, making the system extremely general.

The most recent nonlinear polymers achieve a high nonlinear coefficient,expressed as an r₃₃ of 500 μm/V. Using this in combination with the highsusceptibilities described above, it is believed that it is possibletoday to construct a 1 cm Mach-Zehnder modulator with a V_(π) of 8 mV.This corresponds to a ring resonator with a tuning sensitivity of 795GHz/V. Both of these values are two orders of magnitude better than theperformance obtained by current approaches. Current commerciallyavailable modulators typically have Vπ's from 1 to 9 V, and currenttunable electro-optic polymer based resonators achieve 1 GHz/V oftunability. If the r₃₃ value of 33 μm/V demonstrated by Tazawa andSteier for conventional polymer designs is used, then a V_(π) of 64 mVand a resonator tunability of 50 GHz/V are obtained.

Segmented waveguide contact structures can be formed that allow very lowresistance electrical contact to slot waveguides. We have describedabove, in similar circumstances, electrical contact to waveguides can beestablished via segmented waveguides. See FIG. 12B and FIG. 12D and thediscussion related thereto. When the RC circuits implied by thesegmentation geometry and the gap are examined, it is found that RC turnon times on the order of 200 GHz or more are achievable. Because thenonlinear polymers exhibit an ultrafast nonlinearity, these waveguidegeometries present a path to making Terahertz scale optical modulators.Because the modulation is so strong, it is also possible to trade thelength of the modulator against V_(π). For example, our optimal geometryis expected obtain a V_(π) of 0.6 V with a 100 μm long Mach-Zehndermodulator. This device is expected be exceptionally simple to design for10 GHz operation, as it could likely be treated as a lumped element. Wehave shown above that lateral contact structures with low loss and lowresistance can be constructed with these slot waveguides. See FIG. 12Band FIG. 12D and the discussion related thereto.

We believe these nano-slot waveguide designs present a path to realizingvery high speed, low voltage modulators. It is advantageous to be ableto attain a responsivity V_(π)-L of less than 1 V-cm. The physicalprinciples involved in such devices are based on employing a nonlinearmaterial of at least moderate resistivity, and a high index contrastwaveguide with tight lithographic tolerances. Therefore, it is expectedthat nano-slot waveguides, either as Mach-Zehnder or ring-based devices,are likely an advantageous geometry for optical modulation withnonlinear materials in many situations. In addition, materialscompatibility and processing issues are greatly reduced for such devicescompared to conventional multilayer patterned polymer modulatorstructures.

These high index contrast devices have (or are expected to have)extremely small bend radii, which are often orders of magnitude smallerthan corresponding all-polymer designs with low loss and high Q. Thesegeometric features translate into extremely high free spectral rangesfor ring modulators, compact devices, and wide process latitudes fortheir fabrication. Given the inexpensive and readily available foundrySOI and silicon processes available today, and the commercialavailability of electron beam lithography at sub-10 nm line resolution,it is expected that slot-waveguide based modulators are likely toreplace conventional modulators in many applications in the comingyears.

Waveguide Geometries

We now describe several different waveguide geometries, and show theeffective index susceptibility as a function of the slot sizes of thewaveguide. The susceptibilities are calculated near a 1550 nm free spacewavelength. However, the values obtained will not vary much from 1480 nmto 1600 nm as the modal pattern does not change significantly. In theembodiments described, the waveguides are composed of silicon, andassumed to rest on a layer of silicon dioxide. The top cladding is anonlinear polymer with an index of 1.7. This is similar to the waveguidegeometry that we have used in our modulation work described hereinabove.FIG. 14 shows the static electric fields solved as part of analyzingwaveguide design 1 with a gap of 40 nm, as described in Table 2. As onewould expect, the field is nearly entirely concentrated inside the slotarea. The field shown was calculated assuming a voltage difference of 1Volt. It is slightly larger than simply the reciprocal of the gap sizedue to the singular nature of the solution to Poisson's equation nearthe corners of the waveguide.

FIG. 14A and FIG. 14B illustrate solved field patterns for the analysisof waveguide 1 at a 40 nm gap. FIG. 14A shows the static voltagepotential field distribution due to charging the two electrodes. FIG.14B shows the electric field due to the potential distribution. |E| isplotted in increments of 10%.

We have constrained ourselves to use waveguide geometries that haveminimum feature sizes of at least 20 nm. These are near the minimumfeature sizes that can be reliably fabricated using e-beam lithography.Table 2 lists a description of each type of waveguide studied. Eachwaveguide was studied for a number of different gap sizes. In all cases,the maximum susceptibility was obtained at the minimum gap size. Themaximum gap size studied and the susceptibility at this point are alsolisted. In some cases, the study was terminated because at larger gapsizes, the mode is not supported; this is noted in Table 2. Formultislot waveguide designs where there are N arms, there are N−1 gaps;the design presumes that alternating arms will be biased either at theinput potential or ground.

Table 2 shows the effective index susceptibility for various waveguidedesigns. The susceptibility is approximately inversely proportional togap size.

It is clear that within the regime of slotted waveguides, it is alwaysadvantageous to make the slot size smaller, at least down to the 20 nmgap we have studied. This causes the DC electric field to increase,while the optical mode tends to migrate into the slot region, preventingany falloff due to the optical mode failing to overlap the modulationregion.

TABLE 2 Waveguide Waveguide Arm Sizes Design Height (nm) (nm) Maximum γ(μm⁻¹) Minimum γ (μm⁻¹) 1 100 300, 300 1.3, 20 nm gap .40, 140 nm gap 2150 300, 300 1.6, 20 nm gap .68, 120 nm gap 3 200 300, 300 2.3, 20 nmgap .74, 120 nm gap 4 100 400, 400 1.1, 20 nm gap .67, 60 nm gap, modallimit 5 100 250, 250 1.2, 20 nm gap .56, 60 nm gap, modal limit 6 100300, 40, 300 1.6, 20 nm gap .53, 80 nm gap, modal limit 7 100 300, 40,40, 1.9, 20 nm gap .76, 60 nm gap, 300 modal limit 8 200 200, 40, 200 3,20 nm gap 1.4, 60 nm gap, modal limit 9 300 300, 300 2.5, 20 nm gap 2.5,20 nm gap, modal limit Steier et al. N/A N/A .026, 10 μm gap N/A

In examining the results of our calculations, it is useful to calculatethe maximum susceptibilities that can be obtained. For an effectiveindex of about 2, which is approximately correct for these waveguides,and a gap size of 20 nm, the maximum achievable γ is approximately 12.5μm⁻¹. Thus, for a gap size of 20 nm, waveguide design 8 is alreadywithin 25% of the theoretical maximum value.

It is also worth noting the corresponding γ value that can be obtainedby calculation using our methods for the separated electrode approach ofSteier. The effective index of the mode is expected to be about 1.8, andthe gap distance for the dc field is 10 um. Under the most optimisticassumptions about mode overlap with the active polymer region (that is,assuming complete overlap), this corresponds to a γ of about 0.03 μm⁻¹.

It is useful to calculate, given the current r₃₃ values that areavailable, the index tuning that might be achieved with these designs.The most advanced polymers now yield r₃₃ values of 500 pm/V. If a bulkrefractive index of 1.7 is used, then a ∂n/∂V of 0.006 V⁻¹ is obtainedwith the best design given above. Using a waveguide with an effectiveindex of 2 and a group index of 3, which are typical of silicon-polymernano-slot waveguides, the V_(π) for a Mach-Zehnder with a length of 1 cmis expected to be about 6 mV. The resonance shift that is expected to beobtained in a ring resonator configuration would be 380 GHz per volt.Both of these values represent orders of magnitude improvement in theperformance of these devices compared to current designs.

Segmented Contacting

As we have shown empirically, silicon can be doped to about 0.025 Ω-cmof resistivity with a n-type dopant without substantially increasinglosses. Other dopants or perhaps other high index waveguiding materialsmay have even higher conductivities that can be induced, withoutsignificantly degrading optical performance. However, it is known thatthe conductivity cannot be increased endlessly without impacting opticalloss.

This naturally presents a serious challenge for the issue of driving aslot waveguide of any substantial length. Consider a slot waveguide armof length 1 mm, formed of our optimal design. The capacitor formed bythe gap between the two electrodes is about 0.25 pF. The ‘down the arm’resistance of the structure, however, is 4 MΩ. Therefore, the turn ontime of an active waveguide based on this is about 0.1 μS, implying a 10MHz bandwidth.

A solution to this problem is presented by continuously contacting thewaveguide via a segmented waveguide. This comprises contacting the twosilicon ridges with a series of silicon arms. Even though the siliconarms destroy the continuous symmetry of the waveguide, for the properchoice of periodicity no loss occurs, and the mode is minimallydistorted. This is because a Bloch mode is formed on the discretelattice periodicity, with no added theoretical loss. Of course theperformance of fabricated devices will be different from that ofconventional slot waveguides due to fabrication process differences. Wehave previously demonstrated empirically that continuous electricalcontact can be formed for non-slotted waveguide via segmentation withrelatively low optical losses.

Here we present a simulation of a particular segmentation geometry forour optimal slot waveguide design, that with 200 nm tall and 300 nm widearms and a gap of 20 nm. We have found that a segmentation with 40 nmarms, and a periodicity of 100 nm, appears to induce no loss orsignificant mode distortion in the waveguide. Around 2 um of clearanceappears to be needed from the edge of the segmented waveguide to the endof the arms. FIG. 15A, FIG. 15B and FIG. 15C show plots of several crosssections of the segmented slot waveguide with a plot of the modalpattern overlaid. For comparison, a cross section of the unsegmentedslot waveguide is presented as well. Simulations were also performed toconfirm that the index shift formula continued to apply to the segmentedslotted waveguide. It was found that the index shift was in approximateagreement with the value predicted for the non-segmented case.Non-segmented modesolvers were used for the rest of the simulations inthis work, because simulation of the segmented designs is radically morecomputationally burdensome than solving for the unsegmented case, asthey require solving for the modes of a 3d structure. Since the indexshifts for the unsegmented and segmented cases are extremely similar,solving for the modes in the unsegmented cases is adequate for purposesof design and proof-of-concept.

FIG. 15A shows a cross section of the segmented, slotted waveguide, withthe |E| field plotted in increments of 10% of max value. FIG. 15B showsa similar plot for the unsegmented waveguide. FIG. 15C shows ahorizontal cross section of the segmented, slotted waveguide; Re(Ex) isplotted in increments of 20% of max. In an actual device, some sort ofmetal based transmission line would undoubtedly provide the drivingvoltage for the waveguide. The metal electrodes that would likely formpart of this transmission line have been noted in FIG. 15C. In all casesthe mode has been normalized to have 1 Watt of propagating power. FIG.15A and FIG. 15C show the location of the other respective cross sectionas a line denoted C in FIG. 15A and A in FIG. 15C.

Assuming a 0.025 μl-cm resistivity, one can calculate the outer armresistance as 63 kΩ per side per period, while the inner arm resistanceis 25 kΩ per side per period. The gap capacitance per period is2.5×10⁻¹⁷ Farads. This implies a bandwidth on the order of 200 GHz.

We now describe an electro-optic modulator fabricated from a siliconslot waveguide and clad in a nonlinear polymer. In this geometry, theelectrodes form parts of the waveguide, and the modulator drivingvoltage drops across a 120 nm slot. As a result, a half wave voltage of0.25 V is achieved near 1550 nm. This is one of the lowest values forany modulator obtained to date. As the nonlinear polymers are extremelyresistive, our device also has the advantage of drawing almost nocurrent. It is believed that this type of modulator could operate atexceedingly low power.

A unique advantage with nonlinear polymers is that an integrated opticalcircuit can be conformally coated by a nonlinear polymer. This property,when combined with a slot waveguide, enables the construction of auniquely responsive modulator. We describe the use of a push-pullMach-Zehnder modulator configuration in which each arm has an opposingbias, leading to an opposing phase shift.

FIG. 16A shows the slot waveguide used for the Mach-Zehnder modulator.The modal pattern near 1550 nm is plotted, and contours of |E| areshown. FIG. 16B is an SEM micrograph of a slot waveguide. In this case,the slot waveguide is being coupled to with a ridge waveguide; this modeconverter involves tiny gaps which ensure electrical isolation betweenthe two arms. Contacting arms are also present around 3 μm from theridge/slot junction. The dimensions are two 300×100 nm arms separated bya 120 nm slot.

Nonlinear polymers typically have very high resistivity of 10¹¹ Ωkm. Asa result, the two silicon arms are electrically isolated and can be usedas modulator electrodes. The voltage drop between the arms occurs acrossa 120 nm electrode spacing, as opposed to the 5-10 μm that is typicallyrequired for modulators involving a nonlinear polymer and metalliccontacts. This is a fundamental advantage that slot waveguide geometrieshave for electro-optic modulation.

It is advantageous to contact the silicon arms with an externalelectrode throughout the length of the Mach-Zehnder device to minimizeparasitic resistances. We use a segmented waveguide in which a periodicset of small arms touches both waveguide arms. We use a segmentationwith a periodicity of 0.3 μm and arm size of 0.1 μm that is largelytransparent to the optical mode.

Because the polymer has a second order nonlinearity, a Mach-Zehndermodulator can be operated in push-pull mode, even with no dc bias,effectively doubling the modulator response. FIG. 17A is a diagram ofthe modulator layout, in which contacts A, B, and C are shown. FIG. 17Bis a diagram and FIG. 17C is a SEM micrograph that show the slotted,segmented region, as well as the location where the silicon makescontact with the electrical layer.

Referring to FIG. 17A, there are three regions in the modulator that arecapable of maintaining distinct voltages. During poling operation,contact A is given a voltage of 2V_(pole), contact B a voltage ofV_(pole), and contact C is held at ground. To achieve a poling field of150 V/μm, V_(pole) was 18 V. This has the effect of symmetricallyorienting the polymer in the two Mach-Zehnder arms. During deviceoperation, contact B is driven at the desired voltage, while contacts Aand C are both held at ground, leading to asymmetric electric fields inthe two arms for a single bias voltage. This is the source of theasymmetric phase response. Electrical regions A and C cross thewaveguide by means of a slotted ridged waveguide. At the ridge to slotmode converter, a small gap is left that maintains electrical isolationbut is optically transparent. This enables the device to be builtwithout requiring any via layers. A driving voltage from a DC voltagesource was applied to contact B, while contacts A and C were held atground.

We have recently demonstrated empirically that slot sizes of around 70nm can be fabricated in 110 nm SOI as ring resonators with electricalcontacts. FIG. 18 is a diagram that shows a transmission spectrum of anelectroded slot waveguide resonator with a gap of 70 nm. Fiber to fiberinsertion loss is plotted in dB, against the test laser wavelength innm. We have also confirmed through electrical measurements that the twohalves of the slots are largely electrically isolated.

We believe that there is the possibility of constructing even narrowerslot waveguides, on the scale of 1-5 nm in thickness. For example, onecould use epitaxial techniques to grow a horizontal slot structure(rather than the vertical structures we have explored thus far) with anactive, insulating material, with silicon beneath and above. This couldbe done in a layer form analogous to SOI wafer technology, in which avery thin layer of electroactive material such as the polymers we havedescribed herein could be introduced. Such structures offer thepossibility of yet another order of magnitude of improvement in thelow-voltage performance of modulators. We anticipate our slot structuresto be fairly robust even in the presence of fabrication errors.Fabrication imperfections may cause some of the narrower slots to havetiny amounts of residual silicon or oxide in their centers, or to evenbe partially fused in places. As long as electrical isolation isobtained, and the optical loss is acceptable, we would expect the slotperformance to decrease only in a linear proportion to the amount of theslot volume that is no longer available to the nonlinear polymercladding.

The description provided herein may be augmented by the descriptionsprovided in the following patents and pending patent applications: U.S.Pat. Nos. 7,200,308, 7,424,192, U.S. Patent Application Publication No.2009/0022445A1, U.S. patent application Ser. No. 12/167,063,PCT/US2009/33516, and PCT/US2009/36128.

Now, turning to various embodiments of the instant invention, a LIDARbeam steering device for generating an electromagnetic beam in theoptical domain or mid to near infrared domain (about 10-400 THz,referred to interchangeably herein as “light”) useful for LIDAR, LADAR,as well as other applications, is described herein. The steering deviceis based on a phased array that can be fabricated on a planar photonicintegrated circuit (interchangeably referred to herein as a “chip” or“IC”). The input illumination for the LIDAR beam can be generatedon-chip, by another chip, or by an external laser source where theoutput electromagnetic energy of the external laser source is opticallycoupled into the LIDAR beam steering chip. The input illumination isdivided to provide illumination propagating in a plurality ofwaveguides. The light then is directed through integrated optical phasemodulators. Any suitable optical modulators can be used. Device responsetimes can be well in excess of 10 GHz. Using such phase modulators(typically operated by control electronics), the relative phases of theoptical signal in a number of separate waveguides can be controlled. Thesignals in these optical waveguides can then be directed into couplers,such as, for example vertical couplers, to couple light from thewaveguide mode into a vertically radiating mode providing in totality,an electromagnetic beam. Suitable couplers include, but are not limitedto grating couplers, such as those described by Laere, et al. in“Compact Focusing Grating Couplers for Silicon-on-Insulator IntegratedCircuits,” IEEE Photonics Technology Letters 19, 1919-1921 (2007),etched angled facets, or simple scattering sites. It is contemplatedthat in some embodiments, the optimal size of the vertical mode will beon the order of a few wavelengths of the radiation, or in otherembodiments, perhaps smaller than a single wavelength. The optimal sizeof the vertical mode depends on the specific application and platform.By controlling the phase difference between the scattering sites asdescribed above, the electromagnetic beam can be effectively steeredwith no moving parts.

FIG. 19 shows a diagram of a top view of one exemplary embodiment of aplanar integrated photonic circuit beam steering device 100 suitable foruse in a LIDAR application. In this exemplary embodiment, a 4×4 squarearray of vertical couplers is shown. Other embodiments can have asmaller array or a larger array of couplers. The array can be in ageometrical pattern other than square. Convenient geometries includetriangular or hexagonal arrays. The light source 104 can be either anon-chip light source or an off-chip light source. The outputelectromagnetic beam of the planar integrated photonic circuit beamsteering device 100 (also referred to interchangeably herein as a beamsteering chip) can be steered with no moving parts. Such a steeringdevice 100 can be fabricated on a planar photonic substrate (not shownin FIG. 19) as a phonic integrated circuit. An input waveguide 101formed on the planar photonic substrate can be configured to accept anelectromagnetic energy from a source of electromagnetic energy(radiation) 104. A first splitter 102, formed on the planar photonicsubstrate, is optically coupled to an input waveguide 101 and configuredto split the incoming electromagnetic radiation into one or more paths107. There are four paths 107, shown in the exemplary embodiment of FIG.19. One or more phased array rows 110 are also formed on the planarphotonic substrate (four phased array rows 110 are shown in FIG. 19) andoptically coupled respectively to each of the paths 107. Each phasedarray row 110 includes a row splitter 103. The row splitters 103 areconfigured to split each of the original paths 107 further into two ormore row paths 108. In some embodiments, there can be additionalcascaded row splitters 103 (not shown) and/or row splitters having morethan two split paths (also, not shown).

Each row path 108 includes a phase modulator 105. In FIG. 19, phasedmodulators are shown as groups of four phase modulator channels. It isunimportant to the invention how the phase modulators are grouped duringlayout and for fabrication of a planar integrated photonic circuit beamsteering device 100. Any other suitable groupings can be used. The twoor more phase modulators 105 are optically coupled respectively via arow waveguide 108 to each of the row paths. Each phase modulator output(shown in FIG. 19 optically coupled to waveguide 108 on the right side(output side) of each phase modulator 105) is optically coupled to anoutput coupler 106. Each output coupler 106 is configured to emitelectromagnetic radiation away from the substrate. A plurality ofoptical couplers 106 is configured to radiate a steered electromagneticbeam (photonic beam) in a desired direction away from the integratedphotonic beam steering device 100. For some types of beam formingapplications, it is further contemplated that amplitude modulators canbe added in a path following one or more splitters 103, e.g. in thewaveguide 108 paths.

FIG. 20 shows a side view of an integrated photonic beam steering device100 radiating a steered photonic beam 202 in a direction 203. Thesteered photonic beam 202 is generated by the superposition ofindividual electromagnetic emissions 201 from each coupler 106 onsubstrate 204.

FIG. 21 shows a diagram of a vertical coupling section of a gratingcoupler 301 based beam steering array. Waveguides 108 each feed a phasecoherent optical signal to each grating coupler 301. Grating couplers301 can be formed, for example, by a collection of curved trenches orother scattering sources (not shown in FIG. 21).

It is also contemplated that a chip can be etched at a 45 degree angleto create smaller and more broadband scattering sites. FIG. 22A and FIG.22B show exemplary diagrams of suitable broadband scattering sites. Theprecise angle and configuration of such etching is dependant on theparticular wavelength and material platform. FIG. 22A shows a top andside view of an angle etched (etched angle) vertical scattering site401. FIG. 22B shows a top and side view of an etched facet verticalscattering site 402.

It is also contemplated that edge coupling is suitable for generating asteerable beam. In this approach, the output couplers are placed on theedge of the chip, such as by terminating the waveguides on a cleaved andpolished surface, or by creating a taper on the end of the waveguide. Bycontrolling the phase relation between the output optical modes, asdescribed hereinabove, a beam can be formed that has a particulardirection.

FIG. 23 shows a diagram of one embodiment of an exemplary single-layeredge coupled beam steerable device 500. A top view of the single-layeredge coupled beam steerable device 500 is shown at the top of thedrawing and a side view of the single-layer edge coupled beam steerabledevice 500 is shown at the bottom of FIG. 23. Chip 500 receives anoptical input 502 from either an on or off-chip source of light 502.Input waveguide 509 receives light from optical input 502 and isdisposed on chip substrate 501. Waveguides 503 distribute the light tosplitters 504. Note that there can be branch splitting, such as atbranch splitter 511, before splitters 504.

Each of the phase modulators 505 respectively shifts the phase asdesired to each waveguide 507. The phase shift of each of the phasemodulators 505 is typically controlled by an electronic circuit (notshown in FIG. 23) and each phase modulator 505 outputs a phase shiftedoptical signal to each emitter 506 via each waveguide 507. In theexemplary embodiment of FIG. 23, emitters 506 are shown as having anoptional taper. In some embodiments, emitters 506 can physicallyterminate at a polished edge at a physical edge surface of the chip thusserving as “edge” emitters 506. Any suitable edge emitter 506 can beused. Phase coherent output optical modes 508 result at each emitter506.

To both increase the total amount of output power and to add an abilityto steer the beam in a vertical direction, several beam steering chips,such as for example, beam steering chips 500 as shown in FIG. 23, can bestacked on top of one another. To provide a desired spacing of thestacked layers, each chip 500, while substantially maintaining thedesign shown in FIG. 23, can have a slightly thinned substrate.

FIG. 24 shows a side view of one exemplary stack of edge coupled beamsteering chips 500. The superposition of the plurality of phase coherentoptical modes 508 provides a generated beam 509. Such stacked devices,such as the exemplary device of FIG. 24, are capable of steering a beamin both horizontal and vertical (or two orthogonal) directions.

Further, it is contemplated that both detectors and emitters asdescribed hereinabove can be integrated on the same substrate, forexample, to create a single chip LADAR system. Additionally, beamsteering chips can include coherent and phase sensitive detection.Resolving the delay from when the LADAR beam is transmitted to when itreflects from a distant object is also thought to be possible. This isdue to the fact that the detector electronics can reside in closeproximity to the transmitting circuitry, allowing the use of on-chipphase detection.

As described in greater detail herein, the present invention providesmethods and structures that exhibit enhancement of the nonlinear effectsin various electro-optical materials that is sufficient to make thenonlinear effects accessible with continuous-wave, low-power lasers. Asis described herein the waveguide is coated or clad with anothermaterial which provides or exhibits an enhanced nonlinear opticalcoefficient, such as certain kinds of organic electro-optical materialsthat can be specifically designed to operate in various regions of theelectromagnetic spectrum. It is to be understood that if the highcontrast waveguide core material itself exhibits a sufficiently largenonlinear optical coefficient of the correct order, for example, a χ² ora χ³ coefficient, the cladding may be omitted and the waveguide coreitself can provide the nonlinear optical effects of interest.

Theoretical Discussion

Although the theoretical description given herein is thought to becorrect, the operation of the devices described and claimed herein doesnot depend upon the accuracy or validity of the theoretical description.That is, later theoretical developments that may explain the observedresults on a basis different from the theory presented herein will notdetract from the inventions described herein.

Any patent, patent application, or publication identified in thespecification is hereby incorporated by reference herein in itsentirety. Any material, or portion thereof, that is said to beincorporated by reference herein, but which conflicts with existingdefinitions, statements, or other disclosure material explicitly setforth herein is only incorporated to the extent that no conflict arisesbetween that incorporated material and the present disclosure material.In the event of a conflict, the conflict is to be resolved in favor ofthe present disclosure as the preferred disclosure.

While the present invention has been particularly shown and describedwith reference to the preferred mode as illustrated in the drawing, itwill be understood by one skilled in the art that various changes indetail may be affected therein without departing from the spirit andscope of the invention as defined by the claims.

1. An integrated photonic beam steering device comprising: a planarphotonic substrate; an input waveguide disposed on said planar photonicsubstrate and configured to accept electromagnetic energy from a sourceof electromagnetic energy radiation; a first splitter disposed on saidplanar photonic substrate and optically coupled to said input waveguideand configured to split said electromagnetic radiation into one or morepaths; and one or more phased array rows disposed on said planarphotonic substrate and optically coupled to each of said one or morepaths, each phased array row comprising: a row splitter configured tosplit said each of said one or more paths into two or more row paths;two or more phase modulators, each of said two or more phase modulatorsoptically coupled respectively via a row waveguide to each of said twoor more row paths, each of said two or more phase modulators having aphase modulator output; two or more output couplers optically coupledrespectively to each phase modulator output of said two or more phasemodulators, each of said two or more output couplers configured to emitelectromagnetic radiation away from said substrate, said two or moreoutput couplers configured to radiate a steered photonic beam away fromsaid integrated photonic beam steering device.
 2. The integratedphotonic beam steering device of claim 1, wherein at least one of saidtwo or more output couplers comprises a vertical coupler.
 3. Theintegrated photonic beam steering device of claim 2, wherein saidvertical coupler comprises a grating coupler.
 4. The integrated photonicbeam steering device of claim 3, wherein said grating coupler comprisesa collection of curved trenches.
 5. The integrated photonic beamsteering device of claim 3, wherein said grating coupler comprises acollection of scattering sources.
 6. The integrated photonic beamsteering device of claim 2, wherein said vertical coupler comprises anetched facet.
 7. The integrated photonic beam steering device of claim2, wherein said vertical coupler comprises an etched angle.
 8. Theintegrated photonic beam steering device of claim 1, wherein at leastone of said two or more output couplers comprises an edge coupler. 9.The integrated photonic beam steering device of claim 1, wherein saidedge coupler comprises a cleaved and polished surface.
 10. Theintegrated photonic beam steering device of claim 1, wherein said edgecoupler comprises a taper on an end of a waveguide.
 11. A stackedintegrated photonic beam steering device comprising a plurality ofintegrated photonic beam steering devices as defined by claim 10 andconfigured to emit an electromagnetic beam having phase coherent opticalmodes, said stacked integrated photonic beam steering device configuredto provide a beam that is steerable in two orthogonal directions. 12.The integrated photonic beam steering device of claim 1, wherein saidtwo or more phase modulators comprise a free carrier based integratedoptical phase modulator.
 13. The integrated photonic beam steeringdevice of claim 1, wherein said two or more phase modulators comprise anonlinear polymer integrated optical phase modulator.
 14. The integratedphotonic beam steering device of claim 1, wherein said steered photonicbeam comprises at least one wavelength in wavelength range of about 200nm to 200 μm.
 15. An electronic countermeasure system comprising saidintegrated photonic beam steering device of claim 1, wherein saidsteered photonic beam comprises an electronic countermeasure signal. 16.The electronic countermeasure system of claim 15, wherein saidelectronic countermeasure signal is configured to confuse a missileguidance system.
 17. The electronic countermeasure system of claim 15,wherein said electronic countermeasure signal is configured to confuse aselected one of detection and surveillance system.
 18. An integratedphotonic beam steering system, comprising: a source of electromagneticradiation having a wavelength range in a wavelength range of about 200nm to 200 μm; and an integrated photonic beam steering device accordingto claim 1 coupled to said source of electromagnetic radiation andconfigured to transmit a phase arrayed optical electromagnetic signalsuitable for a selected one of LIDAR and LADAR.
 19. The integratedphotonic beam steering system of claim 18, further comprising: adetector configured to receive a return optical electromagnetic signal,configured to provide phase detection, and configured to measure a delaybetween said transmitted phase arrayed optical electromagnetic signaland said received return optical electromagnetic signal. and a systemoutput configured to provide a measure of said delay.
 20. The integratedphotonic beam steering system of claim 19, wherein said detector isphase sensitive.
 21. The integrated photonic beam steering system ofclaim 19, wherein said detector is disposed on said planar substrate.